Abstract
Pronunciation variation is ubiquitous in the speech signal. Different models of lexical representation have been put forward to deal with speech variability, which differ in the level as well as the nature of mental representation. We present the first mismatch negativity (MMN) study investigating the effect of allophonic variation on the mental representation and neural processing of lexical tones. Native speakers of Standard Chinese (SC) participated in an oddball electroencephalography (EEG) experiment. All stimuli have the same segments (ma) but different lexical tones: level [T1], rising [T2], and dipping [T3]. In connected speech with a T3T3 sequence, the first T3 may undergo allophonic change and is produced with a rising pitch contour (T3V), similar to the lexical T2 pitch contour. Four oddball conditions were constructed (T1/T3, T3/T1, T2/T3, T3/T2; standard/deviant). All four conditions elicited MMN effects, with the T1–T3 pair eliciting comparable MMNs, but the T2–T3 pair asymmetrical MMN effects. There were significantly greater and earlier MMN effects in the T2/T3 condition than that in the reversed T3/T2 condition. Furthermore, the T3/T2 condition showed more rightward MMN effects than the T2/T3 condition and the T1–T3 pair. Such asymmetries suggest co-activation of long-term memory representations of both T3 and T3V when T3 serves as the standard. The acoustic similarity between the activated T3V (by the standard T3) and the incoming deviant stimulus T2 induces acoustic processing of the tonal contrast in the T3/T2 condition, similar to that of within-category lexical tone processing, which is in contrast to the processing of between-category lexical tones observed in the T2/T3, T1/T3, and T3/T1 conditions.
Highlights
In speech communication, pronunciation variation is ubiquitous
The cluster-based permutation test over all frontal-central electrodes revealed that, for mismatch negativity (MMN)-a, the MMN effect reached significance within around 100–280 ms, 140–280 ms, 240–340 ms, and 240–360 ms for T1/T3 (“deviant T3 from T1/T3” vs. “T3 from 100%”, p < .0001), T3 as standard and T1 as deviant (T3/T1) (“deviant T1 from T3/T1” vs. “T1 from 100%”, p < .01), T2/T3 (“deviant T3 from T2/T3” vs. “T3 from 100%”, p < .005), and T3 as standard with T2 as deviant (T3/T2) (“deviant T2 from T3/T2” vs. “T2 from 100%”, p < .05) conditions respectively
Our results showed that the MMNs evoked by the tonal pair T1–T3 peaked earlier than the MMNs evoked by the tonal pair T2–T3 where there is smaller acoustic difference and later identification point
Summary
Pronunciation variation is ubiquitous. A well-documented phenomenon of contextual variation is assimilation, by which a particular phoneme adopts/adapts to the feature(s) of an adjacent phoneme, such as the production of the underlying segment /n/PLOS ONE | DOI:10.1371/journal.pone.0143097 December 1, 2015Allotone with Mismatch Negativity in green boat as a surface [m]-like sound. A well-documented phenomenon of contextual variation is assimilation, by which a particular phoneme adopts/adapts to the feature(s) of an adjacent phoneme, such as the production of the underlying segment /n/. Allotone with Mismatch Negativity in green boat as a surface [m]-like sound. Variation can occur at the supra-segmental level. A lexical tone assigned to a word or morpheme can be realized with different pitch contours contingent upon adjacent tones and discourse context [1,2,3,4]. The question that has received much attention in the literature is how the human brain deals with such variability in the speech signal and what are the neural mechanisms that underlie the representation and processing of speech sounds and their variants
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